Dependency Inversion

dependencies.js

/* This is my file I'll be testing foo.js */

export default function ({ readFileAsync }) {
  return {
    readJsonFile (filePath) {
     return readFileAsync(filePath).then(JSON.parse)
    }
  }
}

/* This is my test file foo.test.js */

import test from 'ava'

import foo from './foo'

test('foo with dependency inversion', function (t) {
  t.plan(2)
  
  const dependencies = {
    readFileAsync(filePath) {
      t.is(filePath, 'bar')
      
      return Promise.resolve('{ success: true '})
    }
  }
  
  const result = await foo(dependencies).readJsonFile('bar')
  t.deepEqual(result, { success: true })
})